Purification of aluminum



p 1950 K. ZIEGLER ETAL 2,952,589

PURIFICATION OF ALUMINUM Filed April 4, 1957 3 Sheets-Sheet 1 Fig.7a

Sept. 13,1960 K. ZIEGLER ETAL 2,952,589

PURIFICATION OF ALUMINUM Filed April 4, 1957 s Sheets-Sheet 2 INVENTORS. M RI. 2756'15, flAHHEfiBEKTlE/MKl/lll Sept- 13; 1 96 K. ZlE-GLER ETAL 2,952,589

PURIFICATION OF ALUMINUM Filed April 4, 1957 a Sheets-Sheet s United States Patent PURIFICATION OF ALUMINUM Karl Ziegler, Kaiser Wilhelm Platz 1, Mulheim (Ruhr), Germany, and Hans-Herbert Lehmkuhl, Mulheim (Ruhr), Germany; said Lehmkuhl assignor to said Ziegler Filed Apr. 4, 1957, Ser. No. 650,709

Claims priority, application Germany Apr. 9, 1956 16 Claims. (Cl. 204-14) This invention relates to new and useful improvements in the purification of aluminum.

With the recent developments in the chemistry of organo-aluminum compounds, various proposals have been made for the recovery of extremely pure aluminum from impure aluminum using organic aluminum compounds such as aluminum alkyls as intermediates.

In accordance with one such proposal, pure aluminum is recovered at the cathode of an electrolysis cell having an anode of impure aluminum and an NaF.2Al(C H electrolyte.

In accordance with another proposal and in contrast to the above-mentioned electrolytic process, pure aluminum is produced in a strictly thermal process. The impure aluminum is dissolved by means of isobutylene and hydrogen forming tri-isobutyl aluminum which is, first of all, thermally decomposed into diisobutylaluminum hydride and iso-butylene and thereafter further decomposed into the pure aluminum, hydrogen and isobutylene.

The above described electrolytic process involves certain dificulties since a current density of more than about 1 ampere per square decimeter cannot be exceeded without mechanically treating the cathode surface during the electrolysis. In addition, the electrolyte has a relatively low conductivity (about 4-10- ohm"- /cm. at 140 C.) so that the cathodes and anodes must be maintained relatively close to each other in the cell in order to obtain the advantage of a small energy consumption. This close proximity of the cathodes and anodes, however, results in difiiculties with respect to maintaining contaminates from the anode away from the cathode.

In the above described thermal process, difiiculties are encountered since large quantities of gas must be handled. For each gram of aluminum formed, 33 normal liters of gas are produced which must be circulated. In addition, difiiculties are encountered in removing the aluminum in a well adhering compact form.

One object of this invention is a combination, nonelectrolytic-electrolytic process for the purification of aluminum without the above-mentioned difiiculties. This, and still further objects, will become apparent from the following description read in conjunction with the drawingsinwhich:

Figure la is a diagrammatic plan .view of an apparatus for effecting the process in accordance with the invention,

Figure lb is a diagrammatic vertical section ofan apparatus for effecting the process in accordance with the invention,

Figure 2 is a diagrammatic plan view of a series of electrolysis cells for effecting the process in accordance with the invention,

Figure 3 is a diagrammatic side elevation of a still further embodiment of an apparatus for effecting the process in accordance with the invention, V

Figure 4 is a diagrammatic vertical section of a still further embodiment of an apparatus for effecting the process in accordance with the invention with the formation of large compact pieces of purified aluminum,

Figure 5a is a diagrammatic side elevation of a still further embodiment of an apparatus for effecting the process in accordance with the invention with the formation of compact purified aluminum bars, and

Figure 5b is a diagrammatic plan view of the apparatusshown in Figure 5a.

In accordance with the invention, the purification of the aluminum is effected by contacting the impure aluminum in a first stage with a lower aluminum trialkyl and hydrogen to thereby form a lower dialkyl aluminum hydride. The lower dialkyl aluminum hydride thus formed in the first stage is mixed with an electrically conductive complex organic aluminum compound forming an electrolyte and the electrolyte mixture or solution thus formed is electrolyzed in a second stage in an anode-cathode containing electrolysis cell forming pure aluminum at the cathode and hydrogen at the anode.

In the first stage the conversion of the aluminum into the soluble organic aluminum compound proceeds in accordance with the equation in which R represents a lower alkyl radical. As the aluminum is not directly converted into a trialkyl alu minum, a special unsaturated hydrocarbon is not re quired and, in addition to the starting aluminum trialkyl, only hydrogen is required.

While any lower aluminum trialkyl, as for example ranging from trimet'hyl aluminum to tributyl or isobutyl aluminum, may be used as the starting aluminum trialkyl, it has been found preferable to use triethyl aluminum since, due to its low molecular weight, it permits the best utilization of the reaction spaces under pressure and is readily obtainable. Trimethyl aluminum, while theoretically being more favorable due to its even lower molecular weight, is not at present as readily available as the triethyl aluminum. As mentioned, other lower aluminum alky-ls, as for example, tripropyl, tri-isobutyl or tri-butyl aluminum may also be used.

The dialkyl aluminum hydrides, such as the diethyl aluminum hydride, thus formed is not a conductor of electricity and therefore cannot be used as such in the electrolysis of the second stage. In accordance with the invention, however, it has been found that by mixing the lower dialkyl aluminum hydrides such as the diethyl aluminum hydride with electrically conductive complex aluminum compounds, and preferably alkali metal organic aluminum compound such as sodium halide, lower aluminum trialkyl complexes, as for example lower alkali metal aluminum tetra alkyl complexes as, for example, sodium aluminum tetraethyl or alkali halide lower dialkyl aluminum halide complexes, as for example KCl.Al (C H 01.

The electrically conductive complex organic aluminum compounds must, of course, be miscible with the dialkyl aluminum hydride forming an electrically conductive mixture or solution having a conductivity, for example, of the order of magnitude of 1-4-10- ohmcm.l. The conductivity of these mixtures or solutions can, furthermore, be favorably affected by increasing the tem perature at which the electrolysis is effected.

Upon the electrolysis in a cathode-anode containing electrolysis cell, very pure aluminum is deposited atvthe cathode and hydrogen form at the anode. The hydrogen should be liberated, i.e., bubble oil the anode so that the anode metal should be one which does not react with hydrogen as, for example, iron, stainless steel or preferably copper or silver. If aluminum anodes are used,- the hydrogen will not be liberated but rather a corresponding Patented Sept. 13, 1960 quantity of aluminum will pass into solution. Aluminum complex aluminum compounds which render the electro lyte conductive, are not changed during the course of the electrolysis. 'The electrolysis is therefore simply a reversal of the formation of the dialkyl aluminum hydrideand for each three mols of the dialkyl aluminum hydride, 2 mols of the trialkyl aluminum, 1.5 mols of hydrogen and 1 gram atom of pure'aluminurn are formed. j

Since the dialkyl aluminum hydride is initiallyproducedfrom aluminum, hydrogen and trialkyl aluminum, the same maybe considered as being produced from aluminum hydride andtrialkyl aluminum and the electrolysis can be considered as nothing more than the breaking down of this aluminum hydride into aluminum and hydrogen. 1 a a a The trialkyl aluminum, such as triethyl aluminum,

liberated during the electrolysis, is not miscible to the same extent with the complex aluminum compounds it which conduct the current as the dialkyl aluminum hydride is. Accordingly, the trialkyl aluminum separates during the electrolysis in the form of an insoluble upper coarsely crystalline powder or else desired.

In normal operation the purified aluminum may be removed from the cathode in a finely crystalline form which becomes more coarsely crystalline as a function of the time during which the same remains in the electrolyte. A purified aluminum powder of the desired crystal size in compact form as v may, therefore, be obtained merely by a suitable selection of the time interval at which the powder is removed from the electrolyte. I

It is also possible to recover the aluminum in a compact form by mechanically pressing the same on the cathode during the electrolysis;

Referring to the embodiment of the electrolysis cell as shown in Figures 1a and lb of the drawings, the cathodes of this cell are in the form of a series of vertically positioned parallel metallic rollers C which are spaced apart a and which do not contact each other. ,These rollers are layer which may still contain small quantities of the dialkyl aluminum hydride. This separated upper layer may very easily be removed from the electrolysis and recycled to the first reaction stage for the reaction with the crude aluminum and hydrogen to form the dialkyl aluminum hydride for the electrolysis.

When considering the process in accordance with the invention as a whole, therefore, the trialkyl aluminum is not consumed and is merely recycled between the stages acting, in effect, as a dissolving intermediate for the aluminum by the hydrogen. Additionally the hydrogen used in the first stage is not lost but is reformed again during the electrolysis at the anode and may be recovered, compressed and reused againin the first reaction stage. The only material that need be supplied to'thereaction is, therefore, the crude aluminum which is conmounted for rotation on suitable" bearings, not shown,- and are rotated preferably at a uniform rate-of speed, byv suitable, drive[,means as, forexample, an electric motor (not shown). Anodes B of, for example, iron,

. stainless steel, copper, some other. suitable metal, are

positioned closely adjacent to the cathodes and have convex curved portions corresponding in shape to the cylindrical shape of the cathodes. On the oppositeside of the anodes,'scrapers A are positioned in contact with the surface of the roller shaped cathodes C so that, as the verted into the purified aluminum. It is thus apparent that the entire process may be considered as a simple formation of aluminum hydride, stabilizedby reaction withthe trialkyl aluminum, and there-decomposition of the aluminum hydride into a purified aluminum and hydrogen with the recycling of the'hydrogen and the trialkyl aluminum to the first stage for the formation of further quantities of aluminum hydride. I v

The electrolysis, in accordance with'the invention, using the lower dialkyl aluminum hydrideelectrically conductive organic aluminum complex electrolyteis highly advantageous, 'Ihe inert metallic anodes may be positioned in the electrolysis cell very close to the cathodes without fear of contamination and the elemental. hydrogen which is liberated will in no way disturb the cathode process. As a result of this, high current densities of .up to 20 amps. per square decimeter, as for example 5 to 20 amps. per square decimeter, may be obtained with low cell voltages, of, for example, 0.5 to 1 volt so that the energy consumption, in the electrolysisis almost insignificant. -With the use of such high current densities, the cells may very easily be constructed'so that, with the use ofcertain additional mechanical measures, the. aluminum may be recovered in a compact form. Additionally the anodes and cathodes may be ideally'shaped with respect to .each other and their function whereas in the purely electrolytic refining with the use of anodes of crude,

aluminum this is'impossible due to the difiiculties en? countered in keeping contaminates from the anode away from the cathode. 7

The purified aluminum maybe recovered in various forms depending upon themode of operation'in accord ance with the invention. Thus, for-example, the refined may be recore'redin the format .a .finely. or.

be hapl cathodes rotate, the scrapers A,will-scrape off the pure aluminum which deposits during the electrolysis.

Thecathodes, and scrapers are positioned in the container X which is filled with the lower dialkyl aluminum hydride-felectrically conductive complex organic aluminum compounds electrolyteso that the liquid electrolyte surrounds the cathode. and is in con tact with-both the cathode and'anode in. the conventional manner. a

gas collector D provided with an exhaust conduit leading, for'example, to a'compressor, may be positioned above the anodes in order to collect the hydrogen evolved during the, electrolysis. The hydrogen so withdrawn and compressed may be. recycled to the first stage forthe formation of the dialkyl aluminum hydride, It is also possible tofill the space above the cathodes with a suitable protectiye gas as, for example, nitrogen. in operation, a direct current is applied across the cathode and anode as the cathodesare rotated in contact with the scrapers A. The pure-aluminum which deposits on .the cathodes as a result of the electrolysis is removed bythe scrapers A and deposited at the bottom ofr the container Xwhich preferably has a troughshapedpchannel for receiving this loose crystalline aluminum. The fineness-ofthe original deposit of aluminum depends upon the current density butas the aluminum is maintainedunderthe liquid electrolyte in the cell, its coarseness increases asanfunctionof time so that-the degree of division ofrthe recovered aluminum can be controlled by. .a suitable .selectionof the period of time during which the same is maintained in theelectrolyte priortoremovaL' i i The aluminum trialkyl whichforms as an upper layer during'the electrolysis may be continuously .or intermittently removed .and' recycled to the'first stage for the formation of dialkyl aluminum hydride and replaced by a corresponding quantity of the dialkyl aluminum hydride msurmgcontinuous operation. a

For .reasons of .economy it is desirable to 'use the highest current densities possible. "The electrolysis cell is, for example, operated atcurrent densities of between 5 and 20 per square deeimeter and the anode may be positioned within a f ew millimeters 0f the'rotating a h W th. a spec fic s nd t tv t e elec ro y 9 *Q c n -*5 fitm nt of 01 m m yb ma ntained {per square decimeter of-electrode surfaceat a voltage or :1..volt. speed:of rotation .of the cathode rollers should, of course, be so adjusted that the growing layer of the loosely adherent aluminum does not reach the anode during one revolution and thus is continuously scraped off before the same will short the anode and cathode.

- It is preferable to effect the electrolysis using a long row of the cells as shown in Figures 1a and 11) positioned one after the other in a closed space which is filled with hydrogen upon the placing of the cells in operation and in which the hydrogen formed upon the electrolysis collects' and may be removed. The hydrogen which collects in this space may be withdrawn by means of a compressor and recycled to the first stage for the production of the dialkyl aluminum hydride.

The troughs at the bottom of the containers X to which the scraped off aluminum collects, may be positioned adjacent to one another forming a common elongated trough from which the aluminum may be continuously or intermittently removed by means of a suitable device as, for example, a conveyor, a scraper flights, a grab bucket, or the like.

As shown in Figure 2, a multiple number of the cells are positioned alongside one another in a long row and provided with a grab bucket G which moves on the crane runway E through the elongated trough formed by the individual troughs of the containers X and removes the loose aluminum which has been scraped off from the cathodes. The time of movement of the grab bucketG may be controlled to obtain the desired crystalline size of the aluminum and the removed aluminum is deposited in the discharge device F as, for example, in the form of a lock chamber which allows the removal of the aluminum without contact with the air. If desired, traces of the electrolyte which still adhere may be washed out from the aluminum by means of a hydrocarbon solvent as, for example, benzene, and the aluminum may be pressed into the form of compact pieces as, for example, in cylindrical molds and thereafter melted down in a suitable manner.

The individual cells may be flow connected so that a common removal of the formed trialkyl aluminum and a common introduction of a corresponding amount of the dialkyl aluminum hydride may be effected.

Instead of cathodes in the form of rotating cylinders or rollers, other moving cathode shapes may, of course, be used. Thus, for example, as shown in Figure 3, the cathode may be in the form of an endless metal belt H which is stretched over to rollers I, at least one of which is driven by suitable drive means as, for example, an electric motor. The anode B is in the form of a suitable screen or grid which extends over the horizontally moving portions of the endless cathode belt H. The deposited aluminum may be removed by the scrapers A and if the scraper A is provided at each reversal point, i.e., at each of the rollers, both sides of the cathode belt H may be utilized for the depositing of the aluminum. The entire arrangement is positioned in a suitable vessel as, for example, one corresponding to the vessel or container X of Figure 1b, immersed in an electrolyte and a direct current potential is applied between the cathode belt H and the anode D.

If it is desired to deposit the purified aluminum on the cathode in a compact form, it is merely necessary to press the same in contact with the cathode surface during the electrolysis as, for example, by means of rollers or the like. This is even desirable at low current densities as, for example, of "the order of magnitude of 1 amp. per square decimeter since even at these low current densities the aluminum layer on the cathode, without mechanical compression, will grow, becoming coarsely crystalline and finally becoming covered with pimply irregularities. As mentioned, for reasons of economy, it is desirable to operate at as high a current density as is possible' and at these higher current densities, the necessity of mechanical pressure in order to obtain a thick layer of aluminum on the cathode is even more pronounced.

The mechanical pressing is most simply done by roll'-; ing the cathodev with a roller of an insulating material as, for example, glass, porcelain, sintered aluminum, hard wood, Teflon or the like. Thus, for example, in Figures 1a and 1b the scrapers A may be replaced by pressure rollers of a suitable insulating material. It is also preferable to provide an arrangement so that the anode and cathodes may move away from each other as the aluminum coating on the cathode rollers increases, thus preventing shorting. Due to the convex shaping of the anode, there is a limitation as to the thickness of the aluminum coating which can be built up in this manner; After the aluminum coating has grown to the desired or maximum size, the same must be removed as, for example, by the removing of the cathodes themselves and replacing with fresh cathodes. If the starting cathodes are themselves pure aluminum, a separation of the deposited aluminum from the cathode is not necessary.

'An embodiment of an apparatus, in accordance with the invention, which is particularly well suited for the production of large compact pieces of refined aluminum, is shown in Figure 4. The cell as shown in the form of elongated, horizontally extending vessel or container X which is provided with a hydrogen outlet at its upper portion leading, for example, to a compressor not shown. The lower portion of the container X is filled with the electrolyte and provided with the flat cathode plate L at the central portion of its bottom.

The anode is in the form of a flat grid or screen which is supported'by means of a frame or chassis mounted on the rollers K of a suitable insulating material.

During operation, the rollers K are rolled back and forth over the cathode L by means of a suitable reciprocating drive, not shown. The direct current is applied across the cathode L and the anode M. The anode M is of a suitable size so that the same will completely cover the cathode L at each limit of back and forth movement of the rollers K and the chassis mounted thereon. In addition, dead spaces with the platforms N are provided on which the rollers K can roll in each direction of movement. The basesN are so provided that the same may be raised to provide a flat rolling surface for the rollers K as the height of the cathode L grows due to the depositing of the aluminum.

The layer of the dialkyl aluminum hydride contain ing electrolyte need, for example, only be a few centimeters above the cathode L. Since distance of the anode M from the cathode L is at all times constant during operation, the layer of aluminum which forms and is compacted on the cathode L may grow to a considerable thickness over a prolonged period of operation.

The diakyl aluminum hydride containing electrolyte is preferably introduced at one side of the cell and removed at the other and the trialkyl aluminum produced is allowed to separate in a special device for this purpose as, for example, a separating vessel, centrifuge, or the like. The electrolyte is then regenerated by the further addition of dialkyl aluminum hydride and recycled to, the cell while the recovered trialkyl aluminum is recycled to the first reaction stage for the formation of further quantities of dialkyl aluminum hydride.

A plurality of cells, as shown in Figure 4, may be arranged in series one behind the other and it is possible, without difiiculty, to produce blocks of the purest aluminum of several square meters surface and a thickness of, for example, 6 centimeters upon continuous operation as, for example, for ten days with a consumption of energy of only about 1 kilowatt hour per kilogram. It is extremely easy, after the long period of operation, to drain the electrolyte from the cell, wash the cell with an inert solvent as, for example, a hydrocarbon, and to remove the aluminum block. The fiat cathode L is advisedly a metal to which the aluminum adheres poorly as, for ex- 7 ample, steel, ste el alloys or the like. Ihe flat beam of the cell itself maybe the cathodeor a removable metal plate maybe placed at the; bottom of the cell and lined: out with the aluminum block and later separated there from. If a cathode plate is used which is, of itself, pure aluminum, a separation is, of course, not necessary.

In the embodiment, as shown in Figures 5a and 5b, an endless rotating belt P is' provided which rotats around two parallel, spaced-apart rollers driven by's'uitable drive means not shown. .A nuihberdof parallel, spaced-apart metal strips which preferably consist 'of-yery pure aluminum are positioned transversely across the belt P and serve as the cathodes. 'Anodes in" the term of grids or screens B are positioned parallel to and slightly spaced from the horizontally extending portions offthe belt P. The belt P and strips 0 pass between two pairs of compression rollers K of suitable i sunnngmateriar In operation, the entire arrangement is immersed in an electrolyte solution in a vessel as, for example, of the type shown in Figure 4 and a direct current potential is applied between theanode B' and the cathode strips '0. The endless belt is rotated by driving one or both of'the spaced-apart rollers and, as the strips pass the anode B,

deposits thereon and is compressed into a compact form by compression rollers K. After the aluminum layer is built up in compacted form ma suitable thickness on the strips '0 the same may be removed at R during operation and fresh strips inserted at Q. If desired, a device maybe provided which will automaticallyremove the strips of a given thickness at "R and replace the same with new cathode plates at Q. If the initial cathode strips consist of the'same very pure aluminum as is ebtained by the electrolytic depositing, the same, uponre- 'moval, may be immediately meltedrfor use or, melted after the removal ofan'y residual electrolyte as, for example, by washing with a hydrocarbon solvent such as benzene. In place of plates, sheets of very purefalumi num may, of course, be producedin the samemanner.

The pure aluminum producediin accordance the mvention'is of excellent quality 'and characterized by an extremely high resistance to corrosion. V a The following'examples are given by way of illustratron and not limitation: i

Example 1 7 Impure aluminum, hydrogen and triethyl aluminum are contacted in a molar ratio of 111.532 forming diethylaluminum hydride. 258 grams 3 grammols) of the diethyl aluminum hydride thus formed is combinedwith 27 0 grams (1 gram mol) of NaF-2Al (C H forming an electrolyte of the composition 1 cathode which is scraped oflF. The aluminum is continuously scrapedfrom the cathodeiremoved from the cell, washed with benzeneto removeany traces ofthe' electrolyte and thereafter pressed and melted and formed into bars which are extremely pure andcorr'osionlresistant.

The hydrogen maybe recovered from the mode by compresslon andrecycled for the contacting with the alumi:

num triethyl. Additionally, during operation of the cell an upper layer of aluminum triethyl forms which may be removedand recycled for contacting'with the hydrogen and crude aluminum for fthe' formation of the diethyl aluminum hydride. A corresponding quantity of the methyl aluminum hydride may be added to the'cell to 8 Example 2" One g am 1 1 0 m l aF ,,(C2H5)a and am 0 14 ram of (CH5)2" e t ing an electrolyte with the composition NaF'-2Al(C H 3 0.5 HAl(C H I 'he diethyl aluminum is formed by contacting hydrogen, triethyl aluminum crude aluminum.

Example 2 is repeated except that the electrolysis is effected with the electrolyte at a temperature of about 150 C. -Pure hydrogen is obtained at the anode and very pure aluminum is deposited at the cathode. The

aluminum may be scraped olf the cathode asa finely crystalline powder, the coarsenessof which increases as the same-is maintainedunder the electrolyte tor a'period of time. r

' Example 4 .One gram mol (354 grams) NaE-2AI(C H and 2 ram mols 228 grams) or HAI(C3H7); are r nte forming an electrolyte of the composition The tripropyl aluminum hydride is initially. formed by contacting impure aluminum, hydrogeni and: tripropyl aluminum. Electrolysis is efiected withthis electrolyte at a temperature of C. in' an electrolysis, cell'using a silver anode and a current density of 5 amps. per square decimeter. Pure hydrogen is generated at the anode and very pure aluminum deposits at thecathode. During'the depositing, the aluminum is continuously compressed by rolling the same with a glass roller. A very compact pure aluminum mass is thus formed at the cathode.

While the invention has been described in' detail with reference to the specific embodiments, various changes and modifications which fall withinthe spirit of the invention and the scope of the appended claims will become apparent to the skilled artisan. i

We claim:

1. Process for the purification of aluminum which comprises contacting the aluminum to be purified with a lower aluminum trialkyl and hydrogen to'thereby form a lower dialkyl aluminum hydride, mixing said lower dialkyl aluminum hydride with an electrically conductive complex organic aluminum compound miscible therewith to thereby form anelect'rolyte, passing an: electric current through said electrolyte between a cathode "and an anode selected from the groupco'nsist'ing fof' silver and copper in an electrolysis cell'to thereby electrolyze'the electrolyte forming pure aluminunfat'the cathode,;hy'- drogen at the anode, and an upperlayer. of'alumin'um trialkyl, and recycling said aluminum *trialkyl 'and said hydrogen formedat the anode for said contacting with the aluminum to be purified to form said lower dialkyl aluminum hydride;

2.1rocess' according to claim .1 inwhich saidcomplex organic aluminum compound is an metal organic aluminum'complen .3. Process accordingto claimil in which said complex organic alurr'tinum compound is a member selected from the group consisting'of sodium halide-lower aluminum 'trialkyl complexes, alk'ali' metal-lower aluminum tetrafiected with this electrolyte at" a tem-' 4. Process according to claim 1 in which said complex organic aluminum compound is NaF.2Al(C H 5. Process according to claim 1 in which said complex aluminum compound is sodium aluminum tetraethyl.

6. Process according to claim 1 in which said aluminum tn'alkyl is triethyl aluminum.

7. Process according to claim 1 in which said electrolysis is eflected with a current density of between about 5 to 20 amps. per square decimeter and a cell voltage between about 0.5 and 1 volt.

8. Process according to claim 7 in which said electrolysis is effected with the anode positioned closely adjacent the cathode in the electrolysis cell.

9. Process according to claim 1 which includes scraping the pure aluminum formed from the cathode during said electrolysis.

10. Process according to claim 1 which includes maintaining the aluminum formed at the cathode in the electrolyte for a period of time sufiicient to increase the size of its crystal structure and thereafter removing the same from the electrolyte.

11. Process according to claim 1 which includes maintaining a protective inert gas above the cathode during said electrolysis.

12. Process according to claim 1 which includes compressing the aluminum formed on the cathode into a compact structure during said electrolysis and thereafter recovering the compacted aluminum.

13. Process according to claim 12 which includes washing the recovered aluminum with a hydrocarbon solvent and thereafter melting the same.

14. Process according to claim 11 which includes recovering said pure aluminum from the cathode, washing the recovered aluminum with a hydrocarbon solvent and thereafter melting the same.

15. Process according to claim 1 in which the aluminum to be purified is substantially continuously reacted with said lower aluminum trialkyl and hydrogen, the hydride formed substantially continuously passed in admixture with an electrically conductive complex organic aluminum compound, the electrolyte thereby formed substantially continuously passed in and out of electrolysis contact with anode and cathode in the electrolysis cell to thereby substantially continuously deposit purified aluminum at the cathode and in which the hydrogen formed at the anode and the aluminum trialkyl formed are substantially continuously recycled for said contacting with the aluminum to be purified to form the lower dialkyi aluminum hydride, the flow of the reactants and the recycling of the hydrogen and the trialkyl aluminumbeing so adjusted that the recycled materials are essentially sufiicient for the first mentioned reaction with continuously newly added aluminum to be purified.

16. Process according to claim 1, in which said complex organic aluminum compound is KCl.Al(C H Cl.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Studies in the Electrodeposition of Metals, Bulletin No. 206, published by University of Illinois, pages 10 and 11.

Angewandte Chemie, vol. 67 (1955), No. 16, pp. 424-426.

Chemical Reviews, vol. 54 (October 1954), pp. 844-845. 

1. PROCESS FOR THE PURIFICATION OF ALUMINUM WHICH COMPRISES CONTACTING THE ALUMINUM TO BE PURIFIED WITH A LOWER ALUMINUM TRIALKYL AND HYDROGEN TO THEREBY FORM A LOWER DIALKYL ALUMINUM HYDRIDE, MIXING SAID LOWER DIALKYL ALUMINUM HYDRIDE WITH AN ELECTRICALLY CONDUCTIVE COMPLEX ORGANIC ALUMINUM COMPOUND MISCIBLE THEREWITH TO THEREBY FORM AN ELECTROLYTE, PASSING AN ELECTRIC CURRENT THROUGH SAID ELECTROLYTE BETWEEN A CATHODE AND AN ANODE SELECTED FROM THE GROUP CONSISTING OF SILVER AND COPPER IN AN ELECTROLYSIS CELL TO THEREBY ELECTROLYZE THE ELECTROLYTE FORMING PURE ALUMINUM AT THE CATHODE, HYDROGEN AT THE ANODE, AND AN UPPER LAYER OF ALUMINUM TRIALKYL, AND RECYCLING SAID ALUMINUM TRIALKYL AND SAID HYDROGEN FORMED AT THE ANODE FOR SAID CONTRACTING WITH THE ALUMINUM TO BE PURIFIED TO FORM SAID LOWER DIALKYL ALUMINUM HYDRIDE. 